2. Seems the location I pointed was wrong and the explanation u gave is helpful.

My goal is to use the IQ signal in L1 band from RFSA. this is why i was trying to use the record and playback application. But if you could mention any other example where i can have the L1 = 1.57542GHz IQ signal using NI RFSA that would be very helpful.

Re: RF Record and Playback Reference Application

Well, if you just want to record IQ data to file then this application should work perfectly fine for 1.57542 GHz collecting. The Reference application records data as Int16 IQ interleaved data (little-endian by default I believe but I've switched it to big-endian in my usage).

It wouldn't take too long for you to modify the niRFSA Simple Record VI to suite your needs if you didn't want to use the entire Record & Playback UI. However, I think the Set RFSA Record Settings VI that pops up before recording is very useful for viewing the signal you want to collect before you actually do.

Regards,

Tim S.

Tim SileoRF Field Account SpecialistNational Instruments

You don’t stop running because you get old. You get old because you stop running. -Jack Kirk, From "Born to Run" by Christopher McDougall.

Re: RF Record and Playback Reference Application

The problem is when i look at the spectrum of the signal given the parameters to generate L1 band signal there is only a single peak which means no indication of mudulated signal (there is a plain sinusoidal signal not mudulated and spread with code as it should be in case of L1 band signal).

Could you please explain why it is so ? is there a problem with the hardware or the software ?

Re: RF Record and Playback Reference Application

I'm not sure why your system isn't seeing the signal since I'm not really familiar with GPS much. Also, there are many factors that could be affecting the ability of your VSA to "see" the GPS signal (i.e. weak GPS receive antenna may cause the GPS signal to be below the noise floor of the VSA or maybe the reference level/bandwidth of the VSA isn't set appropriately...idk).

I found a cool website that has a rough picture of what you should see in the signal's spectra http://eenotebook.co.uk/GPS.htm. Other than that I'm not sure I can be of much more help to you :-). Good luck though.

-Tim S.

Tim SileoRF Field Account SpecialistNational Instruments

You don’t stop running because you get old. You get old because you stop running. -Jack Kirk, From "Born to Run" by Christopher McDougall.

Re: RF Record and Playback Reference Application

Make sure your GPS antenna has a LNA that amplifies your signal before heading to your VSA. Depending on the gain of this LNA, it would be useful to also have the PXI-5690 amplifier on front so that your GPS recording has maximum dynamic range.Take a look at this GPS receiver test application note.

Like Tim is saying, use the Set RFSA Record Settings VI to visualize your signal. Even if it looks very low its ok since GPS signal can be under the noise floor since they have extra 30 dB spreading gain.

1) Simulated. Use the GPS Toolkit to create your own data. Since is software you can do the processing without hardware or you can generated into the VSG to validate it in a different receiver. No point in recording it with VSA.

2) Recorded. You need to recorded "off the air" and not from the VSG. You need an active antenna and the setup that is described on the application note. After successfully recorded the data, you can post process the IQ recorded data.